This invention generally relates to tri-calcium phosphate production. More specifically, the present invention utilizes a production method with a spray head in combination with an agitated air dryer system.
Tri-calcium phosphate is the generic name for precipitated calcium hydroxyapatite. High-quality food-grade tri-calcium phosphate (“TCP”) is used as a calcium supplement in products such as cereals, bakery mixes, dry gravy mixes, spice blends, flours, beverages, animal foods and pharmaceuticals. TCP is also used as an anti-caking agent in salt substitutes, dry beverage mixes, dry soup mixes, dry gravy mixes, spice blends and other hydroscopic food products that require flow conditioning. TCP also serves as a dispersant, a suspension agent for polymerization of styrene, and a ceramic coloring agent.
Currently, TCP slurries are produced by admixing water, hydrated calcium or lime (CaOH), and phosphoric acid in a stainless steel reaction vessel 7 in FIG. 1. A small amount of acetic acid is also added to control the viscosity of the slurry during the reaction and for passage through a surge tank 8. The slurry produced generally has a weight ratio of 72% water and 28% solid TCP. To produce a marketable TCP product, the slurry must be dried to remove the moisture.
The industry standard for removing the moisture is drying the slurry using a combination of steam heated double drum dryers, gas fired flash dryers 12, and air conveyance in FIG. 2. More specifically, drying TCP slurry by spreading it over a steam heated 11 double drum dryer 10 has much inefficiency. The granular characteristics, density and moisture content for different marketable TCP products are determined in the drying process. While the prior art drying techniques produce marketable TCP products, several drawbacks make these techniques less desirable. First, the prior art drying systems utilize a large amount of energy to operate. Approximately 3,750 BTU (British Thermal Units) are required to dry enough slurry to produce one pound of TCP at 2% moisture. The double drum dryer 10 employed has a small production capacity which increases production costs. The drums have a capacity of approximately 800 lbs to 900 lbs per hour. Finally, the double drum drying system generates excessive dust as the dried TCP is scraped from the drums and is dropped into conveyors. The finer particles become airborne and drift onto the surface of the dryer frame, and eventually onto the floor beneath the dryer. This finer material must be collected and disposed of as waste.
Therefore, an efficient TCP production method is needed that utilizes less water and energy for drying TCP to meet commercial needs.